FS library position() to return (size_t) -1 on error

[drmpf]

Fix for error return from position()
PR Issue #9992

Description of Change

Currently FS::position() returns 0 if file is invalid, this change return (size_t) -1 instead, which is a very large number, to indicate an error

Tests scenarios

none

Related links

Closes #9992

[CLAassistant]

All committers have signed the CLA.

[github-actions]

	Warnings
⚠️	Some issues found for the commit messages in this PR: the commit message "position_fix": footer must have leading blank line summary looks empty type/action looks empty Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 20 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).
⚠️	The source branch "PositionFix" incorrect format: contains uppercase letters. This can cause troubles on case-insensitive file systems (macOS). Please rename your branch.

👋 Hello drmpf, we appreciate your contribution to this project!

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Generated by 🚫 dangerJS against 5f586c4

[github-actions]

Memory usage test (comparing PR against master branch)

The table below shows the summary of memory usage change (decrease - increase) in bytes and percentage for each target.

Memory	FLASH [bytes]		FLASH [%]		RAM [bytes]		RAM [%]
Target	DEC	INC	DEC	INC	DEC	INC	DEC	INC
ESP32S3	0	0	0.00	0.00	0	0	0.00	0.00
ESP32S2	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C3	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C6	0	0	0.00	0.00	0	0	0.00	0.00
ESP32H2	0	0	0.00	0.00	0	0	0.00	0.00
ESP32	0	0	0.00	0.00	0	0	0.00	0.00

Click to expand the detailed deltas report [usage change in BYTES]

Target	ESP32S3		ESP32S2		ESP32C3		ESP32C6		ESP32H2		ESP32
Example	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM
FFat/examples/FFat_Test	0	0	0	0	0	0	0	0	0	0	0	0
FFat/examples/FFat_time	0	0	0	0	0	0	0	0	-	-	0	0
LittleFS/examples/LITTLEFS_test	0	0	0	0	0	0	0	0	0	0	0	0
LittleFS/examples/LITTLEFS_time	0	0	0	0	0	0	0	0	-	-	0	0
SD/examples/SD_Test	0	0	0	0	0	0	0	0	0	0	0	0
SD/examples/SD_time	0	0	0	0	0	0	0	0	-	-	0	0
SD_MMC/examples/SD2USBMSC	0	0	-	-	-	-	-	-	-	-	-	-
SD_MMC/examples/SDMMC_Test	0	0	-	-	-	-	-	-	-	-	0	0
SD_MMC/examples/SDMMC_time	0	0	-	-	-	-	-	-	-	-	0	0
SPIFFS/examples/SPIFFS_Test	0	0	0	0	0	0	0	0	0	0	0	0
SPIFFS/examples/SPIFFS_time	0	0	0	0	0	0	0	0	-	-	0	0

[github-actions]

Test Results

 56 files  ±0   56 suites  ±0   5m 11s ⏱️ -7s
 21 tests ±0   21 ✅ ±0  0 💤 ±0  0 ❌ ±0 
135 runs  ±0  135 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 5f586c4. ± Comparison against base commit 4e3523c.

♻️ This comment has been updated with latest results.

[igrr]

Would it make sense to change the return type to ssize_t if we want to return -1?

[me-no-dev]

@igrr it is now exactly the same as in official SD lib. While surely we do agree that unsigned returning -1 is wrong, it is what ends up being done upstream.

[drmpf]

No what is actually being returned here is NOT -1,
but rather ULONG_MAX
i.e. 4294967295
(size_t)-1 is just a short hand.
You can replace it with ULONG_MAX if you wish and still get the same result.

[me-no-dev]

Yes @drmpf , but ULONG_MAX is not an invalid size. It just assumes that you will not have files that are that large.

[drmpf]

Yes but ULONG_MAX a very (edit: unlikely) file position and far more unlikely a return value for a file position than 0.
The only way to avoid that is to use an out-of-band error return like ferror,
as the design of the method does not allow for a separate error turn.
You could change the method to
bool position(size_t &rtn);
but that is not backward compatible.